Orthogonal frequency division multiplexing-code division multiple access system

ABSTRACT

An orthogonal frequency division multiplexing (OFDM)-code division multiple access (CDMA) system is disclosed. The system includes a transmitter and a receiver. At the transmitter, a spreading and subcarrier mapping unit spreads an input data symbol with a complex quadratic sequence code to generate a plurality of chips and maps each chip to one of a plurality of subcarriers. An inverse discrete Fourier transform is performed on the chips mapped to the subcarriers and a cyclic prefix (CP) is inserted to an OFDM frame. A parallel-to-serial converter converts the time-domain data into a serial data stream for transmission. At the receiver, a serial-to-parallel converter converts received data into multiple received data streams and the CP is removed from the received data. A discrete Fourier transform is performed on the received data streams and equalization is performed. A despreader despreads an output of the equalizer to recover the transmitted data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.60/664,868 filed Mar. 24, 2005, 60/665,442 filed Mar. 25, 2005,60/665,811 filed Mar. 28, 2005 and 60/666,140 filed Mar. 29, 2005, whichare incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to a wireless communication system.More particularly, the present invention is related to an orthogonalfrequency division multiplexing (OFDM)-code division multiple access(CDMA) communication system.

BACKGROUND

Wireless communication networks of the future will provide broadbandservices such as wireless Internet access to subscribers. Thosebroadband services require reliable and high-rate communications overtime-dispersive (frequency-selective) channels with limited spectrum andintersymbol interference (ISI) caused by multipath fading. OFDM is oneof the most promising solutions for a number of reasons. OFDM has highspectral efficiency and adaptive coding and modulation can be employedacross subcarriers. Implementation is simplified because the basebandmodulation and demodulation can be performed using simple circuits suchas inverse fast Fourier transform (IFFT) circuits and fast Fouriertransform (FFT) circuits. A simple receiver structure is one of theadvantages of OFDM system, since in some cases only one tap equalizer issufficient to provide excellent robustness in multipath environment. Inother cases, when OFDM is used in conjunction with signal spreadingacross multiple subcarriers, a more advanced equalizer may be required.

OFDM has been adopted by several standards such as Digital AudioBroadcast (DAB), Digital Audio Broadcast Terrestrial (DAB-T), IEEE802.11a/g, IEEE 802.16 and Asymmetric Digital Subscriber Line (ADSL).OFDM is being considered for adoption in standards such as Wideband CodeDivision Multiple Access (WCDMA) for third generation partnershipproject (3GPP) long term evolution, CDMA2000, Fourth Generation (4G)wireless systems, IEEE 802.11n, IEEE 802.16, and IEEE 802.20.

Despite all of the advantages, OFDM has some disadvantages. One majordisadvantage of OFDM is its inherent high peak-to-average power ratio(PAPR). The PAPR of OFDM increases as the number of subcarriersincreases. When high PAPR signals are transmitted through a non-linearpower amplifier, severe signal distortion will occur. Therefore, ahighly linear power amplifier with power backoff is required for OFDM.As a result, the power efficiency with OFDM is low and the battery lifeof a mobile device implementing OFDM is limited.

Techniques for reducing the PAPR of an OFDM system have been studiedextensively. These PAPR reduction techniques include coding, clipping,and filtering. The effectiveness of these methods varies and each hasits own inherent trade-offs in terms of complexity, performance, andspectral efficiency.

SUMMARY

The present invention is related to an OFDM-CDMA system. The systemincludes a transmitter and a receiver. At the transmitter, a spreadingand subcarrier mapping unit spreads an input data symbol with a spreadcomplex quadratic sequence (SCQS) code to generate a plurality of chipsand maps each chip to one of a plurality of subcarriers. An inversediscrete Fourier transform (IDFT) or IFFT unit performs IDFT or IFFT onthe chips mapped to the subcarriers and a cyclic prefix (CP) is insertedto an OFDM frame. A parallel-to-serial (P/S) converter converts thetime-domain data into a serial data stream for transmission. At thereceiver, a serial-to-parallel (S/P) converter converts a received datainto multiple received data streams and the CP is removed from thereceived data. A discrete Fourier transform (DFT) or FFT unit performsDFT or FFT on the received data streams and equalization is performed. Adespreader despreads an output of the equalizer to recover thetransmitted data.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawingwherein:

FIG. 1 is a block diagram of an OFDM-CDMA system in accordance with oneembodiment of the present invention;

FIG. 2 shows the code set of the spread complex quadratic sequence(SCQS) code in accordance with the present invention;

FIG. 3 shows spreading and subcarrier mapping in the system of FIG. 1;

FIG. 4 shows an alternative interpretation of the spreading andsubcarrier mapping in the system of FIG. 1;

FIG. 5 is a block diagram of an OFDM-CDMA system in accordance withanother embodiment of the present invention;

FIG. 6 is a block diagram of an OFDM-CDMA system in accordance with yetanother embodiment of the present invention;

FIG. 7 shows an alternative way for the frequency-domain spreading andsubcarrier mapping in a system of FIG. 6; and

FIG. 8 is a block diagram of an exemplary time-frequency Rake combinerin accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is applicable to wireless communication systemsimplementing OFDM and CDMA such as IEEE 802.11, IEEE 802.16, ThirdGeneration (3G) cellular systems for long term evolution, FourthGeneration (4G) systems, satellite systems, DAB, digital videobroadcasting (DVB), or the like.

The features of the present invention may be incorporated into anintegrated circuit (IC) or be configured in a circuit comprising amultitude of interconnecting components.

The present invention provides an OFDM-CDMA system with an improved PAPRand capacity. The present invention uses a special spreading code, aSCQS code, in spreading input data symbols. The SCQS code comprises twocomponents; a quadratic phase sequence code and an orthogonal (orpseudo-orthogonal) spreading code. Examples of the quadratic phasesequence code, denoted by G, are the Newman phase code (or polyphasecode), a generalized chirp-like sequence (GCL) and a Zadoff-Chusequence. Quadratic phase sequences are called polyphase sequences aswell.

To support a variable spreading factor (VSF), the sequence length of thequadratic phase sequence (or polyphase sequence) is limited as K=2^(k).In some special cases, (such as random access channel or uplink pilots),the sequence length of quadratic phase sequence (or polyphase sequence)can be any arbitrary integer number. Given the number of subcarriersN=2^(n) in the system, consider a sequence length of N as an example.Then, the generic Newman phase code or polyphase code sequence is fixed.The generic Newman phase code sequence is:G _(k) =e ^(−jk) ² ^(π/2) , k=0, 1, . . . , N−1.   Equation (1)

More orthogonal Newman phase code sequences are created by shifting thegeneric Newman phase code sequence in phase. The l-th shifted version,(or DFT modulated), of the generic Newman polyphase code sequence is:G _(k) ^((l)) =e ^(−jk) ² ^(π/2) ·e ^(jkl) ² ^(π/N) , k=0, 1, . . . ,N−1, l=0, 1, . . . , N−1.   Equation (2)Two Newman phase code sequences with different shifts are orthogonal toeach other.

One example of the orthogonal (or pseudo-orthogonal) spreading code,denoted by H, is Walsh-Hadamard code, which is given by: $\begin{matrix}{{H_{2} = \begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}};} & {{Equation}\quad(3)} \\{{H_{2^{m}} = \begin{bmatrix}H_{2^{m - 1}} & H_{2^{m - 1}} \\H_{2^{m - 1}} & {- H_{2^{m - 1}}}\end{bmatrix}},{{{for}\quad m} > 1.}} & {{Equation}\quad(4)}\end{matrix}$

The SCQS code is constructed by combining the quadratic phase code andthe orthogonal (or pseudo-orthogonal) spreading code. For a specificspreading factor 2^(m), the SCQS code has 2^(m) chips. The genericquadratic phase sequence code part of the SCQS code has 2^(m) chips,which is:{G _(i) , G ₂ _(n−m) _(+i) , . . . . , G ₂ _(n−) _(·k+i), . . . , G₂_(m−1) _(+i)};   Equation (5)where k=0, 1, . . . , 2^(m)−1, i=0,1, . . . , 2^(n−m)−1.

The l-th shifted version of the quadratic phase sequence code part has2^(m) chips, which is: $\begin{matrix}{\left\{ {G_{i}^{(l)},G_{2^{n - m} + i}^{(l)},\ldots\quad,G_{{2^{n - m} \cdot k} + i}^{(l)},\ldots\quad,G_{2^{m - 1} + i}^{(l)}} \right\};} & {{Equation}\quad(6)}\end{matrix}$where l=0,1, . . . , N−1, k=0, 1, . . . , 2^(m)−1, i=0,1, . . . ,2^(n−m)−1.

For a specific SCQS code with spreading factor 2^(m), the orthogonal (orpseudo-orthogonal) spreading code part of the SCQS code is given by oneof the codes in the orthogonal (or pseudo-orthogonal) spreading code setof spreading factor 2^(m). For example, the h-th code is denoted by H₂_(m) (h,:).

The k-th chip of the SCQS code c_(i) is constructed as a product of thek-th quadratic phase sequence code of the l-th shifted version of thegeneric quadratic phase sequence code and the k-th chip of the h-thorthogonal (or pseudo-orthogonal) spreading code with the size ofN=2^(m).c _(i) ^(k) =G _(k) ^((l)) ·H ₂ _(m) (h, k), k=0, 1, . . . , 2^(m)−1.  Equation (7)

The code set size of the SCQS code is determined by the code setdimensions of the orthogonal (or pseudo-orthogonal) spreading code partand the quadratic phase sequence code part. The code set dimension ofthe quadratic phase sequence code is fixed regardless of the spreadingfactor and is determined by the number of different shifts, which is thenumber of subcarriers in the system, 2^(n). The code set dimension ofthe orthogonal (or pseudo-orthogonal) spreading code depends on thespreading factor. For example, in the case of a Walsh-Hadamard code, thedimension equals to the spreading factor 2^(m) (0≦m≦n).

Different users are assigned different SCQS codes. In order for areceiver to distinguish between different users, the SCQS codes used bytwo users may be different in the quadratic phase sequence code part,the orthogonal (or pseudo-orthogonal) spreading code part, or both. Thecode set of the SCQS code is shown in FIG. 2.

Without multipath, different SCQS codes are orthogonal as long as theirquadratic phase sequence code parts are different; or an orthogonalspreading code is used. Different SCQS codes are pseudo-orthogonal onlywhen their quadratic phase sequence code parts are the same and apseudo-orthogonal spreading code is used. In both cases, the multipleaccess interference (MAI) between different codes is either zero or verysmall.

Under the multipath fading environment, codes assigned to differentusers should be such that the difference in the shift of quadratic phasesequence code part should be as large as possible. Codes assigned todifferent users should be such that if the difference in the shift ofthe quadratic phase sequence code part of two codes is not less than themaximum delay spread of the multipath channel, there is no MAI betweenthe two codes. Therefore, the corresponding orthogonal (orpseudo-orthogonal) spreading code part can be assigned to be the same.Optionally, the difference in the shift of the quadratic phase sequencecode part may be limited to be at most the maximum delay spread of themultipath channel. This will create more codes with perfect MAIimmunity. This is achievable as long as the number of users in thesystem is no more than N/L, where N is the number of subcarriers and Lis the multipath channel maximum delay spread.

If the difference in the shift of the quadratic phase sequence code partof two codes is less than the maximum delay spread of the multipathchannel, the corresponding orthogonal (or pseudo-orthogonal) spreadingcode part should be different in order to reduce the MAI that cannot becancelled by the difference in the shift of the quadratic phase sequencecode part.

In this way, the MAI can be reduced as compared to the conventional CDMAsystem since the correlation between orthogonal codes is further reducedby the correlation of two quadratic phase sequence codes. For aninterference-limited system (such as CDMA), reduced MAI impliesincreased system capacity.

An OFDM-CDMA system of the present invention comprises a transmitter anda receiver. The transmitter comprises a spreading and subcarrier mappingportion and an OFDM portion. The spreading and subcarrier mappingportion performs spreading of input data symbols into a plurality ofchips and mapping of the chips to one of a plurality of subcarriers. TheOFDM portion performs conventional OFDM operation. The spreading may beperformed in the frequency-domain, in the time-domain or both, whichwill be explained in detail hereinafter.

FIG. 1 is a block diagram of an OFDM-CDMA system 100 in accordance witha first embodiment of the present invention. The system 100 comprises atransmitter 110 and a receiver 150. The transmitter 110 comprises aspreader 112, a serial-to-parallel (S/P) converter 114, a subcarriermapping unit 116, an IDFT unit 118, a cyclic prefix (CP) insertion unit120, a parallel-to-serial (P/S) converter 122 and an optional mixer 124.The spreader 112 spreads input data symbols 101 in frequency-domainusing the SCQS code 111. The procedure of spreading and subcarriermapping is shown in FIG. 3. The spreading factor used by the SCQS codec_(i) is 2^(m) (0≦m≦n). One user can use all of 2^(n) subcarriers in thesystem. Therefore, the number of data symbols that can be transmitted byone user in one OFDM frame is 2^(n−m). Each data symbol d(i) 101 isspread by the spreading code c_(i) 111 into 2^(m) chips 113. The 2^(m)chips 113 are then converted into 2^(m) parallel chips 115 by the S/Pconverter 114 and each chip is mapped to one of the subcarriers 117 bythe subcarrier mapping unit 116 in an equal-distance. The distancebetween each subcarrier used by chips of the same data symbol is 2^(n−m)subcarriers. Chips of different data symbols are mapped to subcarriersin the system sequentially such that the chips of data symbol d(i) aremapped to subcarriers 2^(n−m)·k+i, (k=0,1, . . . , 2^(m)−1, i=0,1, . . ., 2^(n−m)−1).

FIG. 4 shows an alternative embodiment for spreading and subcarriermapping. Instead of the spreader 112, a repeater 402 is used to repeateach data symbol d(i) 2^(m) times at the chip rate. The repeated datasymbols 404 are converted into 2^(m) parallel symbols 407 by the S/Pconverter 406 and each symbol is mapped to one of the 2^(m) subcarriersof equal distance by the subcarrier mapping and weighting unit 408sequentially. The distance between each subcarrier is 2^(n−m)subcarriers. Chips of different data symbols are mapped to subcarriersin the system sequentially such that the chips of data symbol d(i) aremapped to subcarriers 2^(n−m)·k+i, (k=0,1, . . . ,2^(m)−1, i=0,1, . . ., 2^(n−m)−1). A symbol mapped on each subcarrier 2^(n−m)·k+i is weightedby an SCQS code such that a symbol on subcarrier 2^(n−m)·k+i ismultiplied with the k-th chip of the SCQS code, denoted by c_(i) ^(k).

Referring back to FIG. 1, chips 117 mapped on subcarriers are fed intothe IDFT unit 118 to be converted into time-domain data 119. A cyclicprefix (CP) is then added by the CP insertion unit 120 to the end ofeach OFDM frame. The time-domain data with CP 121 is then converted bythe P/S converter 122 into a serial data 123 and transmitted over thewireless channel. It should be noted that the IDFT operation may bereplaced by IFFT or other similar operations and the CP insertion may beperformed after the IDFT output is converted into a serial data streamby the P/S converter 122 and the CP removal may be performed before thereceived signals are converted to a parallel data stream by the S/Pconverter 154.

Due to the structure of spread data, the IDFT operation can besimplified. The output 119 of the IDFT unit 118 comprises data symbolsshifted by a particular phase. The phase is a function of correspondinginput data subcarrier and data symbol indexes. Therefore, the IDFToperation can be replaced by the computation of the phase shift, whichrequires less computation.

For example, assume n/2<m≦n and the orthogonal (or pseudo-orthogonal)spreading code part of the SCQS code are {1, 1, . . . , 1}. Then, theh-th output of the IDFT unit 118 is given as follows: $\begin{matrix}{{{{IDFT}(h)} = {{d(i)} \cdot {\mathbb{e}}^{j\frac{{({{p \cdot 2^{n - m}} + i})}^{2} - 2^{n - 2}}{2^{n}}\pi}}};} & {{Equation}\quad(8)}\end{matrix}$where the value of h satisfies the following condition:h=2^(n−m) ·p+i, p=0, . . . , 2^(m)−1, i=0,1, . . . , 2^(n−m)−1.

It is optional to perform the masking operation at the transmitter 110and the corresponding demasking operation at the receiver 150. Thepurpose of masking is to reduce the inter-cell MAI. At the transmitter110, the mixer 124 multiplies the data 123 with a masking code 125before transmission. The corresponding demasking operation is performedat the receiver 150. A mixer 152 multiplies the received signals 128with the conjugate 151 of the masking code 125 to generate a demaskeddata stream 153.

Referring to FIG. 1, the receiver 150 comprises an optional mixer 152,an S/P converter 154, a CP removing unit 156, a DFT unit 158, anequalizer 160 and a despreader (including multipliers 162, a summer 164and a normalizer 166). The time-domain received data 128 are convertedinto parallel data stream 155 by the S/P converter 154 and the CP isremoved by the CP removing unit 156. The performance of these operationsmay be switched as explained hereinabove. The output 157 from the CPremoving unit 156 is then fed into the DFT unit 158 to be converted intofrequency-domain data 159. Equalization on the frequency-domain data 159is performed by the equalizer 160. As in a conventional OFDM system, asimple one-tap equalizer may be used for the frequency-domain data 159at each subcarrier. It should be noted that the DFT operation may bereplaced by an FFT operation or other similar operation.

Due to the structure of spread data, the DFT operation can also besimplified. The outputs 159 of the DFT unit are data symbols shifted bya particular phase. The phase is a function of corresponding input datasubcarrier and data symbol indexes. Therefore, the DFT operation can bereplaced by the computation of the phase shift, which requires lesscomputation. The way it is done is similar, but opposite, to the IDFToperation at the transmitter side.

The equalized data is despread at the frequency-domain. The output 161at each subcarrier after equalization is multiplied by the multipliers162 with the conjugate 168 of the corresponding chip of the SCQS code,c_(i) ^(k), k=0,1, . . . , 2^(m)−1, used at the transmitter 110. Then,the multiplication outputs 163 at all subcarriers are summed up by thesummer 164 and the summed output 165 is normalized by the normalizer 166by the spreading factor of the SCQS code to recover the data 167.

The receiver 150 may further include a block linear equalizer or a jointdetector (not shown) for processing the output of the despreader. Anytype of block linear equalizer or joint detector may be used. Oneconventional configuration for a block linear equalizer or a jointdetector is the minimum mean square error (MMSE) block linear equalizer.In this case, a channel matrix H is established and computed forsubcarriers, and equalization is performed using the established channelmatrix such that:{right arrow over (d)}=(H ^(H) H+σ ² I)⁻¹ H ^(H) {right arrow over (r)};  Equation (9)where H is the channel matrix, {right arrow over (r)} is the receivedsignal in subcarriers and {right arrow over (d)} is the equalized datavector in subcarriers.

For uplink operation, it is preferred to keep a constant envelope afterIDFT operation, which allows use of an efficient and inexpensive poweramplifier. In order to keep a constant envelope, the followingconditions for a system with N=2^(n) subcarriers have to be met. First,the spreading factor 2^(m) is limited by └n/2┘≦m≦n, wherein the term └a┘means the smallest integer larger than a. Second, for spreading factor2^(m), only a fraction of orthogonal codes are used to combine with thequadratic phase sequence codes to generate the SCQS codes that yieldconstant envelope. For example, in the case of Newman phase code andHadamard code, only the first 2^(┌m/2┐) codes of the Hadamard code sets(of size 2^(m)) are used to combine with the Newman phase sequence codeto generate the SCQS codes. The term ┌b┐ means the largest integersmaller than b.

As stated above, as long as the number of users in the system is no morethan N/L, there is no MAI and there is no need to implement multi-userdetection (MUD). When the number of users in the system is more thanN/L, then there will be MAI and MUD may be implemented. The MAI will bemore benign than conventional CDMA system with the same number of users.

Suppose that there are M users in the system. The number of users forMUD in the conventional CDMA system will be M. However, the number ofusers for MUD in the OFDM-CDMA system in accordance with the presentinvention will be ┌M/L┐, which is reduced by a scale of L as compared toa conventional CDMA system. In this way, the complexity of MUD operationis much lower than the MUD in a prior art CDMA system. It is alsopossible to use multiple antennas at the transmitter and/or receiver.

FIG. 5 is a block diagram of an OFDM-CDMA system 500, (multi-carrierdirect sequence (MC-DS) CDMA system), in accordance with a secondembodiment of the present invention. The system 500 comprises atransmitter 510 and a receiver 550. The transmitter 510 comprises an S/Pconverter 512, a plurality of multipliers 514, a sub-carrier mappingunit 516, an IDFT unit 518, a P/S converter 520, a CP insertion unit 522and an optional mixer 524. If there are N=2^(n) subcarriers in thesystem 500, the N consecutive data symbols 501 of the user i areconverted from serial to N parallel symbols 513 by the S/P converter512. The j-th data symbol of the N parallel data symbols 513 of the useri is denoted by d^(j)(i), where j=0, 1, . . . , N−1. The SCQS code usedby the user i is denoted by c_(i). Each of the N parallel data symbols513 is spread in time-domain using the SCQS code c_(i) 511. Thespreading factor of the SCQS code c_(i) is 2^(m) (0≦m≦n), therefore eachdata symbol 513 is spread by the SCQS code c_(i) 511 into 2^(m) chips515.

At each chip duration, one chip of each of the N data symbols d^(j)(i)is transmitted on its corresponding subcarrier j. One user can use allof 2^(n) subcarriers in the system. Therefore, the number of datasymbols that can be transmitted by one user in one OFDM frame is 2^(n).

The chips 515 are mapped to subcarriers by the subcarrier mapping unit516. Chips 517 on subcarriers are fed into the IDFT unit 518, andconverted into time-domain data 519. The time-domain data 519 areconverted from parallel into serial data 521 by the P/S converter 520,and a CP is added to the end of each frame by the CP insertion unit 522.The data with CP 523 is transmitted over the wireless channel. It isequivalent to perform the conventional DS-CDMA operation on eachsubcarrier independently using the SCQS code, and DS-CDMA signals onsubcarriers are transmitted in parallel using OFDM structure.

The receiver 550 comprises a CP removal unit 554, an S/P converter 556,a DFT unit 558, an equalizer 560, a plurality of rake combiners 562, anda P/S converter 564. First, the CP is removed by the CP removing unit554 from the received data 528 via the wireless channel. The data 555 isthen converted from serial to parallel data 557 by the S/P converter556. The parallel data 557 is fed into the DFT unit 558, and convertedto frequency-domain data 559. Then, equalization is applied to thefrequency-domain data 559 by the equalizer 560. As in a conventionalOFDM system, a simple one-tap equalizer may be used at each subcarrier.

Data 561 on each subcarrier after equalization is recovered by Rakecombiners 562, (which include despreaders), in the time-domain. Then,parallel data symbols 563 yielded by each Rake combiners 562 areparallel-to-serial converted by the P/S converter 564 to recover thetransmitted data.

As in the first embodiment of FIG. 1, it is optional to perform amasking operation at the transmitter 510 and the corresponding demaskingoperation at the receiver 550 to reduce the intercell MAI. The mixer 524multiplies output 523 from the CP insertion unit 522 with a masking code525 before transmission. The mixer 552 of the receiver 550 multipliesthe received signals 528 with the conjugate 551 of the masking code usedat the transmitter 510.

FIG. 6 is a block diagram of an OFDM-CDMA system 600 in accordance witha third embodiment of the present invention. The system 600 comprises atransmitter 610 and a receiver 650. The transmitter 610 includes an S/Pconverter 612, a plurality of multipliers 614, a plurality of repeaters616, a plurality of SIP converters 618, a subcarrier mapping andweighting unit 620, an IDFT unit 622, a P/S converter 624, a CPinsertion unit 626 and an optional mixer 628. In accordance with thethird embodiment, the input data symbol is spread twice, once at thetime-domain and the other at the frequency-domain. Assume the totalnumber of subcarriers is 2^(n) and the spreading factors used in thetime-domain and frequency-domain spreading are 2^(p) and 2^(m),respectively. The N_(T) consecutive data symbols 601 of the user i areconverted from serial to parallel N_(T) symbols 613 by the S/P converter612. The value of N_(T) equals to 2^(n−m). The j-th data symbol of theN_(T) parallel data symbols 613 of the user i is denoted by d^(j)(i),where j=0, 1, . . . , N−1. The time-domain spreading code 611 used bythe user i is denoted by H₂ _(p) (i,:). Each of the N_(T) parallel datasymbols 613 is then spread in the time-domain by the multipliers 614 bymultiplying the symbols 613 with the time-domain spreading code H₂ _(p)(i,:) 611. The spreading factor of the time domain spreading code H₂_(p) (i,:) is 2^(p) as defined in Equations (3) and (4). Each datasymbol 613 is spread into 2^(p) chips and N_(T) parallel 2^(p) chipstreams 615 are generated.

After the time-domain spreading, a frequency-domain spreading isperformed. Given the user i, for each chip stream j, (corresponding tothe j-th data symbols of the N_(T) data symbols), at each chip duration,each chip of the N_(T) chip streams is repeated 2^(m) times by therepeater 616 and the 2^(m) repeated chips are converted into parallel2^(m) chips 619 by the S/P converter 618. The 2^(m) chips are thenmapped to 2^(m) equal-distant subcarriers sequentially by the subcarriermapping and weighting unit 620. The distance between each subcarrier is2^(n−m) subcarriers. Subcarrier mapping is performed sequentially suchthat the repeated chips from the j-th chip stream are mapped tosubcarriers 2^(n−m)·k+j, (k=0,1, . . . , 2^(m)−1, j=0,1, . . . ,2^(n−m)−1). Before the IDFT operation, a chip on each subcarrier2^(n−m)·k+j is weighted by the k-th chip of the SCQS code c_(i), denotedby c_(i) ^(k).

One user can use all of 2^(n) subcarriers in the system. Therefore, thenumber of data symbols that can be transmitted by one user in one OFDMframe is 2^(n−m).

FIG. 7 shows an alternative way for the frequency-domain spreading andsubcarrier mapping in a system of FIG. 6. Instead of repeating the chips2^(m) times, the chips 615 are directly spread by the frequency-domainspreading code c_(i) ^(k). Given the user i, for each chip stream j,(corresponding to the j-th data symbols of the N_(T) data symbols), ateach chip duration, each of the chips 615 is spread by the SCQS codec_(i) ^(k) 703 into 2^(m) chips 704 by the multipliers 702 and thefrequency-domain spread chips 704 are converted into 2^(m) parallelchips 707 by the S/P converter 706. These parallel chips 707 are thenmapped to 2^(m) equal-distant subcarriers 709 by the subcarrier mappingunit 708 sequentially, as explained hereinabove. The distance betweeneach subcarrier is 2^(n−m) subcarriers. Subcarrier mapping is performedsequentially such that the repeated chips from the j-th chip stream aremapped to subcarriers 2^(n−m)·k+j, (k=0,1, . . . , 2^(m)−1, j=0,1, . . ., 2^(n−m)−1).

Referring again to FIG. 6, chips 621 mapped on subcarriers are fed intothe IDFT unit 622, and converted into time-domain data 623. Thetime-domain data 623 is converted from parallel data into serial data625 by the P/S converter 624, and a CP is added to the end of each frameof the data 625 by the CP insertion unit 626. The data with the CP 627is transmitted over the wireless channel.

The receiver 650 includes an optional mixer 652, a CP removal unit 654,an S/P converter 656, a DFT unit 658, an equalizer 660, a plurality oftime-frequency Rake combiners 662 and a P/S converter 664. At thereceiver 650 side, the CP is removed by the CP removal unit 654 from thereceived data 632 via the wireless channel. The data 655 is thenconverted from serial to parallel data 657 by the SIP converter 656. Theparallel data 657 is fed into the DFT unit 658, and converted tofrequency-domain data 659. Then, equalization is applied to thefrequency-domain data 659 by the equalizer 660. As in a conventionalOFDM system, a simple one-tap equalizer may be used at each subcarrier.

After equalization, data 661 on each subcarrier is recovered bytime-frequency Rake combiners 662, which will be explained in detailhereinafter. Parallel data symbols 663 yielded by each of thetime-frequency Rake combiners 662 are then parallel-to-serial convertedby the P/S converter 664 to recover the transmitted data.

A time-frequency Rake combiner 662 is a Rake combiner that performsprocessing at both the time and frequency domains in order to recoverthe data that is spread in both the time and frequency domains at thetransmitter. FIG. 8 shows exemplary time-frequency Rake combiners 662.It should be noted that the time-frequency Rake combiners 662 may beimplemented in many different ways and the configuration shown in FIG. 8is provided as an example, not as a limitation, to those of ordinaryskill in the art.

Each time-frequency Rake combiner 662 comprises a subcarrier groupingunit 802, a despreader 804 and a Rake combiner 806. For each data symbolj (j=0,1, . . . , 2^(n−m)−1) of N_(T) consecutive data symbols, thesubcarrier grouping unit 802 collects the following chips on subcarriers661 2^(n−m)·k+j, (k=0,1, . . . , 2^(m)−1), totaling 2^(m) chips. Then,the despreader 804 performs frequency-domain despreading to the chips onthe 2^(m) subcarriers. The despreader 804 includes a plurality ofmultipliers 812 for multiplying conjugate 813 of the SCQS codes to thecollected chips 811, a summer 815 for summing the multiplication outputs814, and a normalizer 817 for normalizing the summed output 816. Afterthe frequency-domain despreading, chips on 2^(n) subcarriers becomechips on N_(T) parallel chip streams 818. To recover the j-th datasymbol of the user i, time-domain Rake combining is performed by theRake combiner 806 on the corresponding chip stream 818.

Referring again to FIG. 6, it is optional to perform a masking operationat the transmitter 610 and the corresponding demasking operation at thereceiver 650 to reduce the intercell MAI. The mixer 628 multipliesoutput 627 from the CP insertion unit 626 with a masking code 630 beforetransmission. The mixer 652 of the receiver 650 multiplies the receivedsignals 632 with the conjugate 651 of the masking code used at thetransmitter 610.

For all the embodiments described hereinbefore, a predetermined datavector {d(i)}, (i.e., pre-known signals), may be transmitted. In thisway, the uplink transmitted signals can be used as a preamble for RandomAccess Channel (RACH) or uplink pilot signals. For example, apredetermined data vector {d(i)} of all is, {1,1, . . . , 1}, may betransmitted.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

1. An orthogonal frequency division multiplexing (OFDM)—code divisionmultiple access (CDMA) system comprising: a transmitter comprising: aspreading and subcarrier mapping unit for spreading an input data symbolwith a spread complex quadratic sequence (SCQS) code to generate aplurality of chips and mapping each chip to one of a plurality ofsubcarriers; an inverse discrete Fourier transform (IDFT) unit forperforming IDFT on the chips mapped to the subcarriers to generatetime-domain data; a parallel-to-serial (P/S) converter for convertingthe time-domain data into a serial data stream for transmission; and acyclic prefix (CP) insertion unit for inserting a CP into the data; anda receiver for receiving a wireless signal from the transmitter, thereceiver comprising: a CP remover for removing the CP from data in thewireless signal; a serial-to-parallel (S/P) converter for convertingreceived data into multiple received data streams; a discrete Fouriertransform (DFT) unit for performing DFT on the received data streams; anequalizer for performing equalization on an output of the DFT unit; anda despreader for despreading an output of the equalizer.
 2. The systemof claim 1 wherein the spreading and subcarrier mapping unit comprises:a multiplier for multiplying the input data symbol with the SCQS code tospread the input data symbol to generate the plurality of chips; an S/Pconverter for converting the chips into multiple parallel chips; and asubcarrier mapping unit for mapping each chip to one of the subcarriers.3. The system of claim 1 wherein the spreading and subcarrier mappingunit comprises: a repeater for repeating the input data symbol multipletimes at a chip rate; an S/P converter for converting the repeated inputdata symbols into multiple parallel symbols; and a subcarrier mappingand weighting unit for mapping each of the repeated input symbols to oneof the plurality of subcarriers and multiplying each of the repeatedinput symbols with a corresponding chip of the SCQS code.
 4. The systemof claim 1 wherein the spreading and subcarrier mapping unit comprises:an S/P converter for converting N input data symbols into N parallelsymbols; N multipliers for multiplying each of N input data symbols withthe SCQS code to spread the input data symbols; and a subcarrier mappingunit for mapping one chip of each symbol to one of N subcarriers at eachchip duration.
 5. The system of claim 1 wherein the spreading andsubcarrier mapping unit comprises: a first S/P converter for convertingN_(T) input data symbols into N_(T) parallel input data symbols; N_(T)multipliers for multiplying each of the N_(T) input data symbols with atime-domain spreading code, each input data symbol being spread intoSF_(T) chips in time-domain, SF_(T) being a time-domain spreadingfactor; N_(T) repeaters for repeating each of the SF_(T) chips SF_(F)times, SF_(F) being a frequency-domain spreading factor; N_(T) secondS/P converters, each second S/P converter for converting the SF_(F)repeated chips into SF_(F) parallel chips; and a subcarrier mapping andweighting unit for mapping each chip to one of the plurality ofsubcarriers and multiplying each chip with a corresponding chip of theSCQS code.
 6. The system of claim 1 wherein the spreading and subcarriermapping unit comprises: a first S/P converter for converting serialN_(T) input data symbols into N_(T) parallel input data symbols; N_(T)first multipliers for multiplying each of the N_(T) input data symbolswith a time-domain spreading code, each input data symbol being spreadinto SF_(T) chips in time-domain, SF_(T) being a time-domain spreadingfactor; N_(T) second multipliers for multiplying each of the SF_(T)chips obtained in time-domain with the SCQS code to spread the chips,each chips being spread into SF_(F) chips in frequency-domain, SF_(F)being a frequency-domain spreading factor; N_(T) second S/P converters,each second S/P converter for converting the SF_(F) chips obtained fromeach of the SF_(T) chips into SF_(F) parallel chips; and a subcarriermapping unit for mapping each chip to one of the subcarriers.
 7. Thesystem of claim 1 wherein the SCQS code is constructed by combining ageneric quadratic phase sequence code and an orthogonal spreading code.8. The system of claim 7 wherein the SCQS code is constructed bychip-by-chip multiplication of a shifted version of quadratic phasesequence code having 2^(m) chips with one of orthogonal spreading codeswith spreading factor of 2^(m).
 9. The system of claim 8 wherein thequadratic phase sequence code is one of a Newman phase code sequence, ageneralized chirp-like sequence (GCL) and a Zadoff-Chu sequence and theorthogonal spreading code is a Walsh-Hadamard code.
 10. The system ofclaim 8 wherein the chip streams are mapped to subcarriers separated by2^(n−m) subcarriers among a total of 2^(n) subcarriers.
 11. The systemof claim 8 wherein different users are assigned different SCQS codesthat are different in at least one of the quadratic phase sequence codeand the orthogonal spreading code.
 12. The system of claim 8 whereindifferent users are assigned different SCQS codes with a shift as largeas possible in the quadratic phase sequence code.
 13. The system ofclaim 8 wherein the shift of the quadratic phase sequence code islimited to a maximum delay spread of a channel.
 14. The system of claim9 wherein the spreading factor 2^(m) is limited by └n/2┘≦m≦n and onlyfirst 2^(┌m/2┐) codes of the Walsh-Hadamard codes are used to combinewith the Newman phase sequence code to generate the SCQS codes, wherein└a┘ means a smallest integer larger than a and ┌b┐ means a largestinteger smaller than b.
 15. The system of claim 1 wherein the IDFT andthe DFT operation is performed by computing a phase shift using acorresponding input data subcarrier index and data symbol index.
 16. Thesystem of claim 1 wherein the transmitter further comprising a mixer formultiplying a masking code to the serial data stream for transmissionand the receiver further comprising a mixer for multiplying a conjugateof the masking code to the received data.
 17. The system of claim 1wherein the orthogonal spreading code is a pseudo-orthogonal spreadingcode.
 18. The system of claim 1 wherein the IDFT and DFT are performedby an inverse fast Fourier transform (IFFT) and a fast Fourier transform(FFT), respectively.
 19. The system of claim 1 wherein multi-userdetection (MUD) is further performed on an output of the despreader. 20.The system of claim 1 further comprising a block linear equalizer forperforming block linear equalization (BLE) on an output of thedespreader.
 21. The system of claim 1 further comprising a jointdetector for performing a joint detection on an output of thedespreader.
 22. The system of claim 1 wherein at least one of thetransmitter and the receiver comprises multiple antennas.
 23. The systemof claim 1 wherein the input data symbols are predetermined and known tothe receiver.
 24. The system of claim 23 wherein the transmitted signalsgenerated from a predetermined data vector are used as one of a preamblefor random access channel (RACH) and pilot signals.
 25. A method fortransmitting and receiving data using an orthogonal frequency divisionmultiplexing (OFDM)-code division multiple access (CDMA) system, themethod comprising: at a transmitter, spreading an input data symbol witha spread complex quadratic sequence (SCQS) code to generate a pluralityof chips; mapping each chip to one of a plurality of subcarriers;performing an inverse discrete Fourier transform (IDFT) on the chipsmapped to the subcarriers to generate a time-domain data; converting thetime-domain data into a serial data stream for transmission; andinserting a cyclic prefix (CP) to the data; and at a receiver, receivingdata transmitted by the transmitter; removing the CP from the receiveddata; converting the received data into multiple data streams;performing a discrete Fourier transform (DFT) on the multiple datastreams; performing equalization on a DFT output; and despreading theequalized DFT output by multiplying a complex conjugate of the SCQS codeused at transmission with the equalization output and by summingmultiplication results.
 26. The method of claim 25 wherein the spreadingand subcarrier mapping is performed by the steps of: multiplying theinput data symbol with the SCQS code to spread the input data symbol togenerate the plurality of chips; converting the chips into multipleparallel chips; and mapping each chip to one of the subcarriers.
 27. Themethod of claim 25 wherein the spreading and subcarrier mapping isperformed by the steps of: repeating the input data symbol multipletimes at a chip rate; converting the repeated input data symbols intomultiple parallel symbols; mapping each of the repeated input symbols toone of the plurality of subcarriers; and multiplying each of therepeated input symbols with a corresponding chip of the SCQS code. 28.The method of claim 25 wherein the spreading and subcarrier mapping isperformed by the steps of: converting N input data symbols into Nparallel symbols; multiplying each of N input data symbols with the SCQScode to spread the input data symbols; and mapping one chip of eachsymbol to one of N subcarriers at each chip duration.
 29. The method ofclaim 25 wherein the spreading and subcarrier mapping is performed bythe steps of: converting N_(T) input data symbols into N_(T) parallelinput data symbols; multiplying each of the N_(T) input data symbolswith a time-domain spreading code, each input data symbol being spreadinto SF_(T) chips in time-domain, SF_(T) being a time-domain spreadingfactor; repeating each of the SF_(T) chips SF_(F) times, SF_(F) being afrequency-domain spreading factor; converting the SF_(F) repeated chipsinto SF_(F) parallel chips; mapping each chip to one of the plurality ofsubcarriers; and multiplying each chip with a corresponding chip of theSCQS code.
 30. The method of claim 25 wherein the spreading andsubcarrier mapping is performed by the steps of: converting serial N_(T)input data symbols into N_(T) parallel input data symbols; multiplyingeach of the N_(T) input data symbols with a time-domain spreading code,each input data symbol being spread into SF_(T) chips in time-domain,SF_(T) being a time-domain spreading factor; multiplying each of theSF_(T) chips obtained in time-domain with the SCQS code to spread thechips, each chips being spread into SF_(F) chips in frequency-domain,SF_(F) being a frequency-domain spreading factor; converting the SF_(F)chips obtained from each of the SF_(T) chips into SF_(F) parallel chips;and mapping each chip to one of the subcarriers.
 31. The method of claim25 wherein the SCQS code is constructed by combining a generic quadraticphase sequence code and an orthogonal spreading code.
 32. The method ofclaim 31 wherein the SCQS code is constructed by chip-by-chipmultiplication of a shifted version of quadratic phase sequence codehaving 2^(m) chips with one of orthogonal spreading codes with spreadingfactor of 2^(m).
 33. The method of claim 32 wherein the quadratic phasesequence code is one of a Newman phase code sequence, a generalizedchirp-like sequence (GCL) and a Zadoff-Chu sequence and the orthogonalspreading code is a Walsh-Hadamard code.
 34. The method of claim 32wherein the chip streams are mapped to subcarriers separated by 2^(n−m)subcarriers among a total of 2^(n) subcarriers.
 35. The method of claim32 wherein different users are assigned different SCQS codes that aredifferent in at least one of the quadratic phase sequence code and theorthogonal spreading code.
 36. The method of claim 32 wherein differentusers are assigned different SCQS codes with a shift as large aspossible in the quadratic phase sequence code.
 37. The method of claim32 wherein the shift of the quadratic phase sequence code is limited toa maximum delay spread of a channel.
 38. The method of claim 33 whereinthe spreading factor 2^(m) is limited by └n/2┘≦m≦n and only first2^(┌m/2┐) codes of the Walsh-Hadamard codes are used to combine with theNewman phase sequence code to generate the SCQS codes, wherein └a┘ meansa smallest integer larger than a and ┌b┐ means a largest integer smallerthan b.
 39. The method of claim 25 wherein the IDFT and the DFToperation is performed by computing a phase shift using a correspondinginput data subcarrier index and data symbol index.
 40. The method ofclaim 25 wherein the transmitter further performs multiplying a maskingcode to the serial data stream for transmission and the receiver furtherperforms multiplying a conjugate of the masking code to the receiveddata.
 41. The method of claim 25 wherein the orthogonal spreading codeis a pseudo-orthogonal spreading code.
 42. The method of claim 25wherein the IDFT and DFT are performed by an inverse fast Fouriertransform (IFFT) and a fast Fourier transform (FFT), respectively. 43.The method of claim 25 wherein multi-user detection (MUD) is furtherperformed on despreading output.
 44. The method of claim 25 wherein atthe receiver block linear equalization (BLE) is further performed on thedespreading output.
 45. The method of claim 25 wherein at the receiver ajoint detection is further performed on the despreading output.
 46. Themethod of claim 25 wherein at least one of the transmitter and thereceiver comprises multiple antennas.
 47. The method of claim 25 whereinthe input data symbols are predetermined and known to the receiver. 48.The method of claim 47 wherein the transmitted signals generated from apredetermined data vector are used as one of a preamble for randomaccess channel (RACH) and pilot signals.
 49. In an orthogonal frequencydivision multiplexing (OFDM)-code division multiple access (CDMA)wireless communication system, a transmitter comprising: a spreading andsubcarrier mapping unit for spreading an input data symbol with a spreadcomplex quadratic sequence (SCQS) code to generate a plurality of chipsand mapping each chip to one of a plurality of subcarriers; an inversediscrete Fourier transform (IDFT) unit for performing IDFT on the chipsmapped to the subcarriers to generate time-domain data; aparallel-to-serial (P/S) converter for converting the time-domain datainto a serial data stream for transmission; and a cyclic prefix (CP)insertion unit for inserting a CP into the data; and
 50. The transmitterof claim 49 wherein the spreading and subcarrier mapping unit comprises:a multiplier for multiplying the input data symbol with the SCQS code tospread the input data symbol to generate the plurality of chips; an S/Pconverter for converting the chips into multiple parallel chips; and asubcarrier mapping unit for mapping each chip to one of the subcarriers.51. The transmitter of claim 49 wherein the spreading and subcarriermapping unit comprises: a repeater for repeating the input data symbolmultiple times at a chip rate; an S/P converter for converting therepeated input data symbols into multiple parallel symbols; and asubcarrier mapping and weighting unit for mapping each of the repeatedinput symbols to one of the plurality of subcarriers and multiplyingeach of the repeated input symbols with a corresponding chip of the SCQScode.
 52. The transmitter of claim 49 wherein the spreading andsubcarrier mapping unit comprises: an S/P converter for converting Ninput data symbols into N parallel symbols; N multipliers formultiplying each of N input data symbols with the SCQS code to spreadthe input data symbols; and a subcarrier mapping unit for mapping onechip of each symbol to one of N subcarriers at each chip duration. 53.The transmitter of claim 49 wherein the spreading and subcarrier mappingunit comprises: a first S/P converter for converting N_(T) input datasymbols into N_(T) parallel input data symbols; N_(T) multipliers formultiplying each of the N_(T) input data symbols with a time-domainspreading code, each input data symbol being spread into SF_(T) chips intime-domain, SF_(T) being a time-domain spreading factor; N_(T)repeaters for repeating each of the SF_(T) chips SF_(F) times, SF_(F)being a frequency-domain spreading factor; N_(T) second S/P converters,each second S/P converter for converting the SF_(F) repeated chips intoSF_(F) parallel chips; and a subcarrier mapping and weighting unit formapping each chip to one of the plurality of subcarriers and multiplyingeach chip with a corresponding chip of the SCQS code.
 54. Thetransmitter of claim 49 wherein the spreading and subcarrier mappingunit comprises: a first S/P converter for converting serial N_(T) inputdata symbols into N_(T) parallel input data symbols; N_(T) firstmultipliers for multiplying each of the N_(T) input data symbols with atime-domain spreading code, each input data symbol being spread intoSF_(T) chips in time-domain, SF_(T) being a time-domain spreadingfactor; N_(T) second multipliers for multiplying each of the SF_(T)chips obtained in time-domain with the SCQS code to spread the chips,each chips being spread into SF_(F) chips in frequency-domain, SF_(F)being a frequency-domain spreading factor; N_(T) second S/P converters,each second S/P converter for converting the SF_(F) chips obtained fromeach of the SF_(T) chips into SF_(F) parallel chips; and a subcarriermapping unit for mapping each chip to one of the subcarriers.
 55. Thetransmitter of claim 49 wherein the SCQS code is constructed bycombining a generic quadratic phase sequence code and an orthogonalspreading code.
 56. The transmitter of claim 55 wherein the SCQS code isconstructed by chip-by-chip multiplication of a shifted version ofquadratic phase sequence code having 2^(m) chips with one of orthogonalspreading codes with spreading factor of 2^(m).
 57. The transmitter ofclaim 55 wherein the quadratic phase sequence code is one of a Newmanphase code sequence, a generalized chirp-like sequence (GCL) and aZadoff-Chu sequence and the orthogonal spreading code is aWalsh-Hadamard code.
 58. The transmitter of claim 55 wherein the chipstreams are mapped to subcarriers separated by 2^(n−m) subcarriers amonga total of 2^(n) subcarriers.
 59. The transmitter of claim 55 whereindifferent users are assigned different SCQS codes that are different inat least one of the quadratic phase sequence code and the orthogonalspreading code.
 60. The transmitter of claim 55 wherein different usersare assigned different SCQS codes with a shift as large as possible inthe quadratic phase sequence code.
 61. The transmitter of claim 55wherein the shift of the quadratic phase sequence code is limited to amaximum delay spread of a channel.
 62. The transmitter of claim 56wherein the spreading factor 2^(m) is limited by └n/2┘≦m≦n and onlyfirst 2^(┌m/2┐) codes of the Walsh-Hadamard codes are used to combinewith the Newman phase sequence code to generate the SCQS codes, wherein└a┘ means a smallest integer larger than a and ┌b┐ means a largestinteger smaller than b.
 63. The transmitter of claim 49 wherein the IDFToperation is performed by computing a phase shift using a correspondinginput data subcarrier and data symbol indexes.
 64. The transmitter ofclaim 49 wherein the transmitter further comprises a mixer formultiplying a masking code to the serial data stream for transmission.65. The transmitter of claim 49 wherein the orthogonal spreading code isa pseudo-orthogonal spreading code.
 66. The transmitter of claim 49wherein the IDFT are performed by an inverse fast Fourier transform(IFFT).
 67. The transmitter of claim 49 wherein the transmittercomprises multiple antennas.
 68. The transmitter of claim 49 wherein theinput data symbols are predetermined and known to a receiver.
 69. Thetransmitter of claim 68 wherein the transmitted signals generated from apredetermined data vector are used as one of a preamble for randomaccess channel (RACH) and pilot signals.
 70. In an orthogonal frequencydivision multiplexing (OFDM)-code division multiple access (CDMA)wireless communication system where a transmitter spreads an input datasymbol with a spread complex quadratic sequence (SCQS) code to generatea plurality of chips and maps the chips to a plurality of subcarriersusing OFDM, a receiver comprising: a CP remover for removing a CP fromreceived data; a serial-to-parallel (S/P) converter for converting thereceived data into multiple received data streams; a discrete Fouriertransform (DFT) unit for performing DFT on the multiple received datastreams; an equalizer for performing equalization on an output of theDFT unit; and a despreader for despreading an output of the equalizer.71. The receiver of claim 70 wherein multi-user detection (MUD) isfurther performed on an output of the despreader.
 72. The receiver ofclaim 70 further comprising a block linear equalizer for performingblock linear equalization (BLE) on an output of the despreader.
 73. Thereceiver of claim 70 further comprising a joint detector for performinga joint detection on an output of the despreader.